PHOENIX — The 1.5 million residents of Phoenix were warned Tuesday to boil their drinking water or use bottled water as a precaution because of problems at treatment plants, and to take conservation measures.

Muddy water stirred up by recent storms was flowing into one of the city's two operating water-treatment plants, reducing the output of that plant, officials said.

Two other treatment plants were shut down for maintenance, and the fifth was closed because it was flooded by the storms, leaving only one of the city's five water-treatment plants producing at full capacity.

Cloudy water coming from taps does not necessarily have serious health effects, said Annie DeChance, a spokeswoman for the Phoenix Water Services Department.

However, the suspended particles causing the cloudiness could interfere with water disinfection, provide a medium for bacterial growth, and indicate the presence of disease-causing organisms.

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"Some particles that make it through the filtering process could contain bacteria," DeChance said. "It's hard for us to tell, that's why we're telling everyone to boil their water."

Mayor Phil Gordon said tests Tuesday showed the water was safe. He said the recommendation to boil the water was a precaution until final test results become available Wednesday.

"We're asking everyone not to panic, not to overreact," Gordon said at a news conference. "We expect everything is fine. We believe everything is fine."

City Manager Frank Fairbanks said the city passed 102 of 103 federally mandated water tests, failing only a test that detects the number of particles in the water.

"Obviously there's some reason the test is needed, but it isn't like we have arsenic or lead in the water," he said.

Besides boiling water for drinking, residents were told to take short showers, shut off landscape watering and use bottled water for brushing teeth, making ice, preparing food and washing dishes.

At Sky Harbor International Airport, food was prepared early Tuesday with bottled water and only bottled beverages were served.

Other cities that receive some water from Phoenix, including the suburbs of Mesa, Tempe and Scottsdale, were using alternate water sources Tuesday.